When an electric current is passed through a light-emitting diode using an organic light-emitting diode (OLED) as a semiconductor material, holes generated from an anode and electrons generated from the cathode recombine in a light-emitting layer with the release of photons. By adjusting the energy released by electron-hole pair recombination in the OLED device, photons with different energies corresponding to different colors of light may be emitted. An organic light-emitting display panel using an OLED device as a display material has many advantages, such as self-luminous, wide viewing angle and high contrast, etc., and has been widely used in smart products, such as a mobile phone, a digital video camera, and a laptop computer, etc. Because of its light weight, thin thickness, and flexibilities, the organic light-emitting display panel becomes a research focus.
The organic light-emitting device often has a sandwich structure with electrodes on both sides and an organic functional layer sandwiched there between. Light is emitted from a transparent or a translucent electrode. Indium tin oxide (ITO) is often used as an anode for the OLED device due to its high light transmittance in the visible range, desired conductivity and holes injection capability. For the material of the organic functional layer, film is generally formed by vacuum deposition and spin-coating processes. A cathode of the OLED device is often formed by deposition or sputtering using materials with low work function, such as aluminum, zinc, lead or calcium, etc.
FIG. 1 illustrates a schematic diagram of a basic structure of an existing OLED device. Referring to FIG. 1, the OLED device includes an anode 011′, a hole transport layer 012′, a light-emitting layer 013′, an electron transport layer 014′ and a cathode 015′ from bottom to top. Based on the above structure of the OLED device 01′, due to the introduction of the hole transport layer 012′, the electron transport layer 014′ and other various organic functional layers, the thickness of the OLED device 01′ is equal to the value of the light wavelength. Meanwhile, a semi-reflective electrode (i.e., one of the anode 011′ and the cathode 015′) can be regarded as a semi-reflective film, and the reflective electrode (i.e. the other of the cathode 015′ and the anode 011′) can be regarded as a full-reflective film. Therefore, the OLED device 01′ with such structure has a micro-cavity effect to some extent. Due to the high quality factor of the micro-cavity structure, a high-intensity and long-life light field may be formed inside the micro-cavity.
Due to the angle-dependent characteristics of the micro-cavity structure of the OLED, the brightness and the light-emitting color of the organic light-emitting display panel fabricated using the above OLED device vary with the viewing angle. To solve such technical issue, a film layer with high refractive index and low absorption rate as a light-coupling layer is deposited outside of a light-emitting side electrode (the semi-reflective electrode) of the organic light-emitting display panel, thereby improving the light transmittance of the organic light emitting display panel and the light-emission efficiency of the device without affecting the electrical performance of the device.
However, the improvement of the light-emission efficiency by using one light-coupling layer is rather limited. Therefore, how to provide an organic light-emitting display panel and a display device capable of further improving the light-emission efficiency is an urgent issue to be solved. The disclosed organic light-emitting display panel and device are directed to solve one or more problems set forth above and other problems.